The present invention relates to a cable holder, an more particularly, to a cable holder that is capable of securing the cable airtightly by clamping in the axial direction.
Cables, cords and electric conductors (hereunder collectively referred to as cables) are guided to switch boxes through holders mounted on the wall of the switch boxes. In order to prevent moisture from entering the switch box through the cable holding or clamping portion, the holder must secure the cable airtightly. Many holders have been developed to achieve this purpose, and one such cable holder is disclosed in U.S. Pat. No. 4,373,112. The cable holder of this U.S. patent consists of a hollow cylindrical body to be mounted on a switch box through which the cable is inserted. Part of this cylindrical body is surrounded by the bended portion of a U-shaped belt clamper, the belt wings of which are urged by engagement between a bolt and nut. By screwing the bolt into the nut, the belt wings come closer so that the bended portion of the clamper clamps the cylindrical body to secure the cable to said body.
While this type of holder ensures reliable fixing of cables, the operator must handle the bolt and nut not in the axial direction of the cable, but in a direction vertical to the cable axis, and depending on the place where the cable is used, a screw driver may not be able to have an access to the bolt, and this makes it substantially impossible to execute the clamping operation.
Therefore, cable holders of the type that can clamp the cable by screwing in the axial direction of the cable have been developed.
Typically, a cable holder of this improved type consists of a hollow cylindrical body provided with a female or male thread through which the cable is inserted, a hollow screw cap or chuck having a male or female thread that engages with the female or male thread formed on said hollow cylinder, and a clamper or gripper that is mounted within the hollow cylinder and by which the inserted cable is clamped. As the screw cap is threaded into or onto the hollow cylindrical body, the inside diameter of the gripper which is made of a resilient material decreases by a sufficient degree to urge the cable toward its center and hold it in position. If this urging of the cable toward its center is uniform throughout the circumference of the cable, the clamper will ensure the airtight holding of the cable. In this case, if the clamper and/or any part that cooperates with it has a small opening in the axial direction for receiving the cable, the latter cannot be easily inserted into the holder with the clamper or its associated part accommodated therein. To avoid this problem, the clamper is made of an elastically deformable material such as rubber which enables gradual insertion of the cable and which, upon the threading of the screw cap, deforms elastically to urge the periphery of the cable toward the center. Typically, a cable holder of the type described above consists of a hollow cylindrical member having a male thread, a hollow screw cap in a nut form that engages said male thread, and a resilient clamper or gripper that is detachably or permanently mounted on the hollow cylindrical member. The inner wall of the unthreaded portion of the cap nut forms a conical surface tapered toward the opening into which the cable is inserted. As the cap nut is threaded onto the hollow cylinder, the inner conical surface of the nut urges the clamper inwardly to reduce the inside diameter of the clamper until the cable is securely held. In this case, the reduction in the inside diameter of the clamper has a substantially linear relationship with the decrease in the outside diameter of the clamper. As a result, the clamping of the cable requires rotating the cap nut a number of times and, toward the final stage of the clamping operation, the cap nut must be given a particularly powerful rotation.